1. Field of the Invention
The present invention relates to a device and a method for determining the self-motion of a vehicle in an environment.
2. Description of Related Art
Methods for determining the self-motion of a vehicle are known. Methods of this type are to be classified under the subject area of “sighted cars,” although these methods may be applied to a variety of vehicle types in principle. These methods are based on recording the environment in which the vehicle is moving with the aid of imaging methods and processing it computationally. The environment, including the objects located therein, is analyzed on the basis of the analysis of the image data, and the driver of the vehicle is provided with additional data, for example, regarding the occurrence of obstacles or the approach of other vehicles. In order to analyze the image data regarding such information which is important to the driver and his/her driving behavior, the analysis of the image data regarding the instantaneous direction of travel of the vehicle, among other things, is of importance. A point or an area toward which the vehicle seems to be steering is regularly ascertained with the aid of a snapshot produced by an imaging device. This point or area is referred to as focus of expansion (FOE). It is the projection of the direction of movement of the camera on the image plane. Since the instantaneous image shows only part of the environment, the center of expansion does not necessarily need to be located within the image section of the snapshot. For example, in the case of a rotary motion, the center of expansion is in infinity in the corresponding direction of rotary movement. To ascertain the center of expansion, the optical flow, among other things, of selected (or all) image points of the snapshots between two snapshots taken at two separate points in time is determined. In simple terms, this means that the direction and absolute value of the motion of the image points over time is ascertained. The optical flow of an image point may also be understood as a motion vector. Stationary points, i.e., points or structures (image features) that do not move in consecutive snapshots are relevant for determining the center of expansion. The optical flow of such points may be zero, almost zero, or less than a defined threshold value. Stationary points may arise by the observed structures being located so far from the imaging device that their relative motion is negligible (background structures). Furthermore, stationary points may arise by an observed object not moving relative to the camera, as is the case, for example, of parts of the host vehicle or a preceding vehicle traveling in the same direction at the same velocity. In particular in traffic it seldom happens that these stationary points are actually stationary for a longer period of time, since, for example, the vehicle may turn a corner, the preceding vehicle which up to that point was traveling at a constant speed may accelerate or brake, or a stationary point located far away may be hidden by a vehicle cutting in. Methods according to the related art do not provide a satisfactory method for ascertaining the self-motion of the vehicle quickly and reliably, particular in rapidly changing environments.